Animal nervous systems are not ‘new’


  • Early forms of sense-react existed in prokaryotes


  • During the Cambrian explosion, specialized nervous systems appeared
    • allowed animals to sense environment
    • allowed animals to respond quickly


  • Cnidarians are the simplest organisms with nervous systems
    • nerve nets
    • contraction & expansion of gastrovascular cavity

Nervous systems consist of circuits of neurons and cells

  • In complex animals, axons of many neurons are bundled into ‘nerves’


  • Fibrous- like nerves channels information flow along targeted routes in the nervous system


  • Nerve circuits differ across the animal phylogeny
    • sea stars = radial nerves connected to central ring
    • bilaterial animals - cephalization

Central nervous systems (CNS)

  • Many animals have neurons that carry out integration (i.e., perception) formed into a CNS


  • Planaria (flat worms) represent the first defined CNS
    • small brain and nerve cords
    • only a few hundred neurons



  • Higher animals have more complicated brains and nerve cords with ganglia

Peripheral nervous system (PNS) relays info to CNS

Nervous system organization matches lifestyle

Vertebrate nervous system

  • CNS develops from hollow dorsal nerve cord
    • central canal of spinal cord
    • ventricles of brain


  • Brain & spinal cord have grey and white matter
    • grey = neuron cell bodies, dendrites, axon terminals
    • white = bundled axons


  • White matter exists on the interior of brain where neuron signalling is turned into function
    • learning, emotions, processing, etc.


  • White matter exists on the outer layer of the spinal cord to link CNS with PNS

Spinal cord relays info to and from brain

Also, acts independently for simple rapid reflexes

PNS plays a large role in animal movement/homeostasis


  • Sensory information reaches the CNS along PNS neurons
    • afferent neurons = to carry towards


  • CNS processes information and instructions travels to muscles, glands, etc.
    • efferent neurons = to carry away


  • Nerve bundles include afferent and efferent neurons

PNS plays a large role in animal movement/homeostasis


  • PNS has 2 efferent components
    • motor system
    • autonomic nervous system


  • Motor system carry signals to skeletal muscles
    • voluntary (raise a hand)
    • involuntary knee-jerk


  • Autonomic system regulates involuntary smooth and cardiac muscles
    • Sympathetic, Parasympathetic, Enteric
    • Enteric = digestion, pancreas, gallbladder

Sympathetic and Parasympathetic are antagonistic

Arousal and energy generation (symp) vs calming and self-maintenances (para)

Vertebrate brain is specialized by region


Forebrain = processing of smells, sleep regulation, learning and complex processing


Midbrain = routing of sensory input


Hindbrain = involuntary activities such as blood circulation


Across vertebrates, sizes of each region reflect importance of functions

Birds and mammals have larger brain:body size ratios

Human brain


100 billion neurons make 100 trillion connections


Cerebrum is essential for language, cognition, memory, consciousness and awareness

Human brain


100 billion neurons make 100 trillion connections


Cerebrum is essential for language, cognition, memory, consciousness and awareness


  • Cerebrum is also regionized
    • Frontal lobe = temperament and decisions
    • Temporal lobe = hearing
    • Paretial lobe = touch and integration
    • Occipital lobe = vision

Body parts are connected through sensory and motor cortexes

Limbic system responsible for behaviorial, emotions, memory




  • Hippocampus = memory center (short and long)
    • looks like a seahorse


  • Amygdala = emotional responses, including pleasure, fear, anxiety and anger
    • looks like an almond
    • emotion functions in robust memories